nucleus

Definition: The cellular organelle in eukaryotes that contains the genetic material.

The major components of the nucleus are chromosomes, chromatin, which are dense strands of nucleoprotein fibers holding the genetic material of the cell, and the nuclear matrix, which is a protein-containing fibrillar network. Nucleoli are electron-dense structures that function in the synthesis of ribosomes and rRNA. The fluid suspension of the nucleus is called the nucleoplasm, in which the solutes of the nucleus are dissolved.